Hydroxyindole-O-methyltransferase (HIOMT), catechol-O-methyltransferase (COMT) and histamine-N-methyltransferase (HNMT) in the pineal gland of the vizcacha (Lagostomus maximus maximus).

The activities of three methylating enzymes HIOMT, COMT, and HNMT were determined in pineal glands from 2 groups of adult vizcachas of both sexes, one (I) maintained under permanent lighting (15 days) and the other (II) kept in darkness. The control determinations (III) were carried out in pineal glands from animals hunted and killed during the night. In (I) the HIOMT activity decreased and the COMT activity increased; no changes were exhibited by HNMT. In (II) showed a diminished HIOMT activity. In captivity illumination affected HIOMT and COMT activites in a similar form to that observed in other species of rodents. The decrease in HIOMT activity in (II) suggests that captivity may affect pineal function, possibly as a consequence of a decrease in locomotor activity.